[Methodologic aspects of quality assurance in veterinary epidemiological studies]. / Methodische Aspekte zur Qualitätssicherung veterinärepidemiologischer Studien.

In planning and conducting epidemiological studies the quality of the investigation should be sufficient to take care that all possible conclusions are correct. In this paper we deal with these parts of epidemiological studies which are related to quality and therefore have to be under control. This is done in the view of veterinary medicine.

Investigation of the pathogenesis of transplacental transmission of Aleutian mink disease parvovirus in experimentally infected mink.

The transplacental transmission of Aleutian mink disease parvovirus (ADV) was studied in experimental infection of 1-year-old female non-Aleutian mink. The ADV-seronegative female mink were inoculated with ADV prior to mating or after the expected implantation of the embryos during pregnancy. A group of uninfected females served as a control group. Animals from each group were killed prior to or shortly after parturition. The in situ hybridization technique with radiolabeled strand-specific RNA probes was used to determine target cells of virus infection and virus replication. In both infected groups, ADV crossed the endotheliochorial placental barrier, although animals infected before mating already had high antibody titers against ADV at the time of implantation. The percentage of dead and resorbed fetuses was much higher in dams infected before mating. In the placentae of these mink, virus DNA and viral mRNA were detected in cells in the mesenchymal stroma of the placental labyrinth and hematoma but only occasionally in the cytotrophoblast of the placental hematoma. Placentae of animals infected during pregnancy showed in addition very high levels of virus and also viral replication in a large number of cytotrophoblast cells in the placental hematoma, which exhibited distinct inclusion bodies. In both groups, neither virus nor virus replication could be detected in maternal endothelial cells or fetal syncytiotrophoblast of the placental labyrinth. Fetuses were positive for virus and viral replication at high levels in a wide range of tissues. Possible routes of transplacental transmission of ADV and the role of trophoblast cells as targets for viral replication are discussed.

Diagnosis of fetal infection with porcine parvovirus by in situ hybridization.

In situ hybridization (ISH) for the diagnosis of fetal infection with porcine parvovirus (PPV) was compared with immune electron microscopy (IEM) and serology by immunofluorescence (IF) for its sensitivity and its applicability in a routine diagnostic laboratory. The technique was applied to the examination of sections of formalin-fixed paraffin-embedded tissues from 68 fetuses. Fifty-three of these fetuses were diagnosed serologically since they had a crown rump length of more than 17 cm, i.e. they were mature enough to mount a humoral immune response; 38 were positive and 15 negative. Eleven out of 15 smaller fetuses examined for the presence of viral antigen by immune electron microscopy (IEM) were positive and 4 were negative. Heart and lung were found to be the most suitable organs for in situ hybridization. In situ hybridization yielded a positive result in 8 of the 11 IEM positive fetuses and in 33 of the 38 serologically positive fetuses. No signal was detected in any of the 4 IEM or the 13 serologically negative fetuses. Expenses for IEM were estimated to be 179% of the expenses for ISH. Expenses for serology by IF on the other hand were 67% of the expenses for ISH. From this it was concluded that the most efficient way to diagnose a fetal infection with PPV was serology by IF, if possible with samples from several fetuses and that the other techniques, IEM or ISH, ought to be reserved for those cases where no immunocompetent fetuses were available for diagnosis.

[The infectious causes of abortion and stillbirth in swine in Switzerland]. / Untersuchungen zu infektiösen Ursachen für Aborte und Totgeburten beim Schwein in der Schweiz.

Fetuses and placentae of 171 cases of porcine abortion, stillbirth and mummification were examined for pathological lesions, bacterial infections and PPV (porcine parvovirus) infection. Furthermore IgG (immunoglobulin G) levels were determined in fetal body fluids. Selected maternal sera were tested for antibodies against Leptospira, Aujeszky's disease and hog cholera. PPV infection was diagnosed in 29.2% of all cases. Bacterial abortion was diagnosed in 8.2%. Indications for an infectious agent were demonstrated in about 10% of the cases. The etiology of the abortion could not be identified in 52%. Inflammatory alterations in association with the isolation of bacteria consisted of neutrophilic infiltration and necrosis and were of particular value to differentiate bacterial contamination from infection. Infiltrations of mononuclear leucocytes in brain, leptomeninx, kidney or myocard were observed in about 50% of the fetuses with PPV infection. IgG levels were consistently elevated in fetuses serologically positive for PPV, but also in two fetuses, where no infectious agent could be identified.